A vehicle suspension system is to provide a comfortable ride to a vehicle passenger and improve a driving performance of the vehicle. To the purpose, the vehicle should be effectively shielded from the impact of the force generated due to an irregular road surface condition, whereby a vehicle operator keeps the vehicle under control comfortably, maintaining a good grip and getting a good feedback from the vehicle.
Such a vehicle suspension system has been developed to better passenger's comfort and improve the driving performance by employing an active toe angle adjustment mechanism. A difference between a steer angle of an inside wheel and that of an outside wheel defines a toe angle. The active toe angle adjustment mechanism controls the toe angle therebetween. Such an active toe angle adjustment mechanism is recently adopted for rear wheels as well as front wheels of a vehicle. FIG. 1 shows a suspension system employing a conventional toe angle adjustment mechanism for a rear wheel 1.
Rotationally coupled to the rear wheel 1 is a steering knuckle 2, which is pivotally connected with a first control arm 4, a second control arm 6, and a trailing arm 8. Arranged generally longitudinal to the vehicle is the trailing arm 8 and traverse to the longitudinal centerline thereof are the first control arm 4 and the second control arm 6. The second control arm 6, used for adjusting the steer angle of the rear wheel 1, is connected with a hydraulic linear actuator 7 having a fixing rod 10, which is pivotally connected with a rear cross member (not shown) of a vehicle body (not shown).
The suspension system further includes a shock absorber 5 and a spring 3 assembled together to vertically support the steering knuckle 2. The shock absorber 5, mounted between the steering knuckle 2 and the vehicle body, serves to dampen vertical vibration of the vehicle body, together with the spring 3.
FIG. 2 illustrates the hydraulic linear actuator 7, which includes a cylinder 11, a cap 12, a piston rod 13, a piston 14, and the fixing rod 10. The cylinder 11 has an open end hermetically covered by the cap 12 and a closed end integrally formed with the fixing rod 10. One end of the piston rod 13 hermetically passes through the cap 12 and coupled with the piston 14 disposed inside the cylinder 11, while the other end thereof is connected with the second control arm 6. The piston 14 partitions an inner space of the cylinder 11 into a first chamber 17 and a second chamber 18.
Respectively disposed near the closed end and the sealed end of the cylinder 11 are a first port 15 and a second port 16. Hydraulic pressure is selectively applied to the piston 14 via the first and the second port 15 and 16. The piston 14 while being in equilibrium is sustained at the center of the cylinder 11 by a first and a second elastic member 19 and 20, which are disposed at the first chamber 17 and the second chamber 18, respectively.
Hydraulic pressure applied via the first and the second port 15 and 16 is adjusted by using a hydraulic valve 21, which is electrically controlled by an electronic control unit (ECU). Based on a signal from a steering angle sensor 23 and/or a vehicle speed sensor 22, e.g., a speedometer, the ECU controls the operation of the hydraulic valve 21. That is to say, the speed sensor 22 and the steering angle sensor 23 provide feedback information of the vehicle's driving condition to the ECU, which in turn controls the hydraulic valve 21 such that the hydraulic linear actuator 7 can actively adjust the toe angle of the rear wheel 1.
The above-explained conventional toe angle adjustment mechanism employing the hydraulic linear actuator can be problematic in that the hydraulic units, i.e., the hydraulic linear actuator, occupy relatively large space and yield slow response time. Further, such a hydraulic control system can be fairly complex, involving relatively large number of complicated parts, and, therefore, limiting a production yield.